^ Personally, I hate the Diablos as much as the Barioth.
I'll start by listing the attacks it uses most: charge, hip check, tail whip, Diablos' tail whip, Diablos-used-dig!, uppercut. Bite's a joke.
Charge should be easy to see coming because it'll spam this like crazy. Dodge off to the side or whatever because it can't change direction midway. After the charge ends, though, watch out for that waving tail. It's still an active hitbox.
Hipcheck always gave me a problem because I barely, and rarely, had time to either block or skip away. Barioth+ is honestly your best bet for going up against Diablos because the evasion ups you get really help. Given that the Diablos has wide, sweeping attacks, you can either easily roll through those or right under it's body. Or you could guard. Or get hit. Your call.
Diablos does the standard tail whip (whirl around) and then it has it's own version of tail whip. You can either wait it out or roll in between it's legs. Legs are a safe spot for almost any monster that uses tailwhip, so that's a plus.
Uppercut, again, dodge it. Be careful, though, because that tail is an active hitbox. I know I've evaded the horns and gotten slapped by the tail. It's hax.
As for Diablos-used-dig!, just keep running. it'll home in onto you, and it can change it's path midway. Toss a sonic grenade just as it disappears underground to trap it. Hack away.
Keep in mind: once Blos' horns are broken, it takes longer to dig. Even so, make the tail your first priority. Once the tail is out, a lot of Blos' attacks lose their followup edge. Then, focus on the horns. Best way I like to lick it with my friends: keep bashing it and once it's fatigued, sonic as it tries to dig, pitfall trap it, have a hammer user KO it, add shock trap before it can dig away again and that's a ton of damage done.
Timing's hard to get down, though. Diablos is more of a hit-and-run kind of guy, so act accordingly. Oh, and it's always a good idea to bring dung bombs. Just saying.
Okay, so get this. I went 0/4 on ANY Diabolos Fangs. I kept getting ridges and crap, but no Fangs!? So I had to master the art of slaying Diabolos.
10 Sonic Bombs + 1 Pitfall Trap + Thunderclap = easy. Is it cheap? Yes. Did it work? In 18 minutes, 3 times in a row.
So I got Crit Draw on GS Set, and Thundddaaaclap+
All I've got left offline is Rathalos, Bariaoth(sp), and whatever's after that. HR is 4, and I'm getting a 2nd copy so me and my girlfriend can play online together. Would love friends :]
(I main LS with SA and GS on the side, she does SA with LS on the side)
Off of all this, I'm running these three sets:
LongSword!
Full Lagi, Thunderclap+, crap Assessory with 1 slot (need better one). Lagi is lv6 all the way, and I have Speed Sharpner and Health+20 Gemed (Can't get anything better gemmed yet besides health)
So I have
Razor Sharp(Blue Sharpness!), Speed Sharp, Oly. Swimmer, Elem. Dmg up, Health+20, and whatever else the set gives.
Switchaxe
Aiming to farm full Rathalos, with a Crit. Eye assessory added will have Att up Med, Crit+2, and Speed Sharpener. Currently have Bolt Axe.
Great Sword
Wearing Full lagi (Speed Sharp) and Diablos hands w/ assessory for CE at the moment, but aiming for:
Full Punishing Draw set bar-hands, D hands, whatever lagi sword, and then Punishing draw gemmed in if needed.
I don't know what PD does, but I've heard the both together own.
Anyways, any tips or feedback would be nice^^
Edit: I did kill Blos a couple times without item whoring, so I'm not an ubernoob.